An insulation treatment is applied to a motor typically mounted in hybrid electric vehicles having a generator that generates electric power based on engine driving or regeneration, and a motor that operates using power supplied from a battery to drive driving wheels, or electric vehicles including such hybrid vehicles.
However, because a motor driven in hybrid electric vehicles or electric vehicles as described above has a higher voltage than a typical motor, and is at, for example, 500 V, when the hybrid electric vehicles or electric vehicles travel in, for example, a high-altitude area (for example, at high elevations above 4000 m), the pressure near the motor decreases, resulting in a situation where electronic discharge tends to occur in the air, and an insulation treatment film applied to the motor may deteriorate to cause insulation defects. Further, an inverter-driven motor may transiently have non-uniform voltage sharing, which concentrates voltage at a first coil that is closest to the inverter, and discharge may tend to occur.
Heretofore, there have been proposed devices that prevent entrance of water or dust resulting from a situation where a wheel motor of an electric vehicle has an internal pressure lower than an external air pressure. For example, Japanese Patent Publication No. JP 2005-153724 A proposes a system having a flood sensing means for sensing flooding of a motor for the purpose of water proofing, wherein the inside of the motor is pressurized in accordance with the output of the flood sensing means, and Japanese Patent Publication No. JP 4-185533 A proposes a structure wherein compressed air is supplied into a wheel motor from an air tank mounted in a vehicle so that a wheel motor internal pressure is made higher than an external air pressure by 0.02 MPa or more.
However, even if the inside of the motor is pressurized at the time of flooding, or a wheel motor internal pressure is made higher than an external air pressure by 0.02 MPa or more, the wheel motor internal pressure may be at one atmospheric pressure (0.1 MPa) or less when the vehicle travels in a high-altitude area, and in such cases, discharge may still occur, and a motor insulation treatment film may deteriorate.